In the internal combustine engine fuel supply system, vaporization of fuel constitutes one of the serious problems. Vaporization results from heating of fuel due to heat generated from the engine. It not only obstructs the supply of fuel, but the vapor thus produced is forced into the carburetor so that the air/fuel ratio is changed and thus adversely affects the engine operation.
As a means for preventing vapor from being supplied to the carburetor, there is provided a return system. In the return system, the outlet chamber of the fuel pump is provided with a return pipe communicating with the fuel tank for returning vapor, and extra fuel if necessary, to the fuel tank. Such a known return system is shown in FIG. 1 but, as explained hereinafter, it does not sufficiently avoid the vapor problem.
This invention thus relates to a diaphragm-type fuel pump which incorporates an improved vapor return system associated therewith.